function wp_snippet_maintenance_mode() {
if ( !current_user_can( 'edit_themes' ) || !is_user_logged_in() ) {
wp_die( '<strong>Site offline for maintenance!</strong><br/>Hang on - we´ll be right back online.<br/>For contact & support - please refere to: <a href="http://www.wp-snippet.com" target="_blank" rel="noopener noreferrer">http://www.wp-snippet.com</a> !', 'Site Offline For Maintenance', '');
}
}
add_action('get_header', 'wp_snippet_maintenance_mode');